This invention relates to communication systems including radar systems, and more particularly, to a virtual noise waveform as generated by a radar system. The waveform has no detectable attributes discernible by radar signal detection and analysis equipment. This allows a radar system utilizing the waveform to obtain desired intelligence without disclosing either the presence of the radar or whose radar it is.
A primary usage of radar systems is intelligence gathering. In a military or covert operations setting, this requires a radar platform to interrogate an area of interest using radar signals which are transmitted at a target, and to receive return signals which can be processed to obtain the desired information. Different radar systems have different signal characteristics or attributes. These include, for example, whether the radar is pulsed or continuous wave (CW), its energy, operating frequencies, frequency hop rates, chip rates, coding schemes, etc. A conventional radar system typically generates a high energy, uncoded signal which is readily detectable with the appropriate equipment. Radar systems used for military or covert purposes employ different schemes to hide or disguise their transmitted signals. For example, a covert radar signal will have less radiated energy than a conventional signal, and employ a different coding scheme. Regardless, it has been found that these signals, too, are detectable. It will be understood that while the attributes or signal characteristics of one radar system may significantly vary from those of another, the characteristics of each represent an individualized signature. Accordingly, someone detecting a radar signal above some threshold in a radar band and performing appropriate signal analysis can readily determine not only that intelligence gathering is taking place, but also who is doing it.
Detection avoidance techniques are well-known in the art. Among detection avoidance methods employed by current radar systems are the use of terrain masking, power management, adaptive scanning, pulse compression, and frequency diversity techniques. Terrain masking (which has been ostensibly used since World War II) requires an airplane, for example, to fly close to the nap of the earth. Power management involves the radar generating only the signal power necessary for a particular task. Adaptive scanning involves transmitting radar signals only on a limited basis, and then focusing the transmission only in the target direction. Pulse compression techniques are used to distribute the transmissible energy over time; while, frequency diversification involves spreading the available energy over a wide spectrum. While each of these techniques has certain advantages which to some extent may mask a radar, implementation of any of these avoidance strategies still results in a radar waveform having an identifiable set of characteristics. If the waveform is detected despite any of the avoidance strategies employed, the waveform characteristics will again provide a signature by which the source of the radar signal can be determined. It would be greatly advantageous and desirable to employ a radar system having detection avoidance capabilities in which a signal waveform would have no discernible attributes from which would aid in the detection of the source of the signal.